Preparation Of Rare Earth Doped LAS Miccropowders By Polyacrylamide Gel Method And Crystallization Behavior

Li₂O-Al₂O₃-SiO₂(LAS) glass-ceramics as one of the most important system glass-ceramics has some excellent properties such as low thermal expansion coefficient, tolerance for high temperature and heat impact etc. Those excellent properties attract many scientists'attentions recently. At present, the production cost and energy consumption are too high for LAS glass ceramic and enhancing its performance is too difficult. The preparation of homogeneous fine LAS micropowders has been considered to solve the issue. Therefore, it is essential to study the process of LAS multicomponent glass-ceramic crystallization and the effect of rare-earth on crystallization process.In this paper, Acrylamide, N,N`-methylene-bisacrylamide, nitrates of aluminum, lithium carbonate, and tetraethoxy silane are used as material. Lithium aluminosilicate (LAS) multicomponent glass-ceramic powders were prepared by using polyacrylamide gel method and calcining at high temperature. The composition of samples, which were doped with three kinds of rare earth oxide and prepared under different temperature and different mass, was characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Crystallization mechanism was discussed.The results indicate that the distribution of ions is homogeneous in solutions easily gelled by in situ formation of polyacrylamide gels. The unique crystallization mechanism of the polyacrylamide gel method comparing with other routes is derived from the simultaneous development of [SiO4] and [AlO4] tetrahedrons.The main crystal phase and crystallization sequence of LAS micropowders have no change with additions of Eu₂O₃,Gd₂O₃ or Er₂O₃. But the crystal amount ofβ-spodumene increased, which indicated the crystallization temperature decrease. LAS multicomponent glass-ceramic powders increased with the heat treatment temperature going up. Hexagonal structureβ-quartz solid silution was detected at 700℃. Someβ-spodumene characteristic peaks appeared at 800℃, and the main crystal phase was converted to tetragonal at 900℃.The result of FT-IR indicated that rare earth oxide, at the range from 0 to 2.0mol%, did not enter into the structure net of LAS powder, but acted as network modifier. It made the bond length and bond angle of Si-O-Al change, and had the influence on crystallization process.The influence of Gd₂O₃ retraining phase ofβ-quartz solid solution and promoting phase ofβ-spodumene was most, when LAS powder prepared by polyacrylamide gels doped with Eu₂O₃,Gd₂O₃,Er₂O₃.